Electrical-discharge device.



W. C. WHiTE.

ELECTRICAL DISCHARGE DEVICE.

APPLICATION FILED MAR. 20. 19l4.

Patented Nov. 2, 1915.

300 l77/cro Amps.

His Attorney Inventor. Willim Chit/e,

the metal electrodes.

UNITED STATES PATENT omeE.

WILLIAM C. WHITE, 01 SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

Specification 0! Letters Patent.

Patented Nov. 2, 1915.

Application filed March 20, 1914. Serial No. 826,027.

To all whom it may concern:

Be it known that I, WILLIAM C. WHITE, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in Electrical-Discharge Devices, of which the following is a specification.

My present invention comprises certaln improvements in vacuum electrlcdevlces and is of particular value in connectioirwlth the detection ofhigh frequency oscillations used in electro-magnetic wave signalingsystems.

My improved detector is in constructlon somewhat similar to the well-known audion set forth in U. S. patent to De Forest #879,532, and isalso similar in construction to the vacuum tube device described andclaimed in an application filed by Irving Langn'iuir, October 16, 1913,Serial No. 795,610. In both of these prior devices an exhausted glasstube is provided having a cathode adapted to be heated to incandescenceby some suitable source of current, an anode or plate connected in alocal circuit with one terminal or leg of the incandescent cathode, anda conductor or grid located in .proximity to the cathode and upon whicha varying potential is impressed, the variations of which afi'ect theamount of currentflowing in the vacuum space between the cathode and theplate or anode. The change in current in this local circuit bears nonecessarily definite relation to the change of potential on the grid,but is very greatly affected by the nature of the vacuous space in whichthe electrodes are located. Thus, in the vacuum relav or amplifier ofthe type shown in the said Langmuir application, the tube is exhaustedto the highest possible *degree of vacuum, the gas being driven out ofthe walls of the tube as well as out of all of tions the current flowinthe tube between the incandescent cathode and the plate or anode,isdue to a pure electron discharge from-the heated cathode, and is notdependent iupon the presence of residual gas as a conducting medium. Ina tube thus highly exhausted. current in the local circuit or platecircuit increases with increase of grid potential and decreases withdecrease of grid; potential, but the difference in the amount ofincreasefor a given variation of potential is not so' far different from Underthese condi-' the decrease caused by a decrease of grid potential as tomake the device a good detector of high frequency oscillations. In otherwords, the asymmetry of current flow in the local circuit due to aseries of high frequency oscillations is not sufliciently great toenable the device to operate effectively in connection with a telephoneor other receiver for detecting such high frequency impulses. The deviceis more especially valuable as a relay or amplifier of suchoscillations. If, however, a certain amount of residual gas be presentin the tube then the operation of the device becomes quite diiferent.Such a construction and mode of operation is that characteristic of theso-called audion. In the audion, if very low voltage be used in thelocal or plate circuit, the device is relatively very insensitive, or inother words, the change of current in the local circuit is very smallfor a given change of potential on the grid. The device becomes moresensitive as the voltage inthe local circuit is increased. Thereis alimit however to the voltage which may be used in the local circuitbecause as the voltage is increased, ionization of the gas in the tubeincreases, a blue glow appears followed by deterioration of theelectrodes, disenga'gement'of more gas therefrom and finally destructionof the operative qualities of the tube. The voltage impressed on thelocal circuit is therefore made as high as possible consistent with theavoidance of these limited conditions. In the apdion as thusconstituted, a decrease of potential on the grid causes a decrease ofcurrent in the local circuit while increase of potential on the gridcauses an increase of current in the local circuit, but the decrease ofcurrentis of ,a magnitude very much greater than the increase of currentcaused by an increase of potential on the grid. The' result is that whenhigh frequency oscillations are impressed upon the grid their presenceis made known by a decrease of current in a device such as disclosed inthe hangmuir application, very remarkable results are secured in therelations which then exist between the current in the plate circuit andthe changes of potential on the grid. With this definite pressure of gasor vapor in the device, I have found that the variation of current inthe plate circuit with variation of potential on the grid follows thelaw of a pure electron discharge. tube such as that of the Langmuirapplication, except within a small range of voltage in the platecircuit. Within this small range there appears to be a condition ofinstability such. that when high frequency oscillations are. impressedupon the grid there always follows a sudden decrease of current in thelocal circuit. The explanation of this phenomenon is decidedly obscurebut the existence of the phenomenon is very real. Within the range ofvoltage indicated, the application of high frequency oscillations or ofcontinuous high frequency waves, causes the current in the local circuitto decrease so suddenly that a very distinct signal is pro- 'duced inthe telephone receiver or other indicating device in the .local circuit.The sharpness of the'signal thus produced .is such that my improveddevice is not only extremely sensitive to. receive high fre-' quencyimpulses but because of the sharpness of the signals the effect ofstatic is not nearly so serious as in "other detecting devices.

While my improved detector is dependent upon the presence of a small butdefinite gas pressure in the space including the electrodes, itsoperation is not accompanied by blue glow or any other Well recognizedevidemos of positive gas ionization. The amount ofgas or vapor presentis perhaps not more than of that which characterizes the .so-calledaudion.

The sensitiveness of my improved devices varies with the potentialimpressed upon the gridand becomes a maximum at a certain definitepotential. To secure this maxirgun sensitiveness a definite potentialwhich varies according to the particular device is impressed upon thegrid circuit. As this potential is changed by the high frequencyoscillations, the current 1n the plate circuit is, suddenly decreased,thereby producing the desireds'gna'l. v

a In produciilg and maintaining the desired gas pressure in my notsuflicient to leave in the tube a certain amount of residual gas duringexhaustion since this gas does not remain constant in punt but generallywill decrease upon opx I device by the well-known ielaenrau a t o thoughin, Qm $S,, h amount of gas prcsentincreasesrather than jt crea s iidaet r a s es sur he fiedes s'ary near-1a gas or vapor pressure inordinary improved device it is manner the tube, I therefore provide asubstance with the desired vapor pressure and place "this in the tube.Among other things I have found that amalgam is suitable for thepurpose. Mercury alone appears to be unsuitable, as it has too high avapor pressure at temperatures though by lowering the temperature of themercury the desired vapor pressure maybe obtained.

The novel features of my invention are pointed out with greaterarticularity in the appended claims, and" or a better understanding ofmy invention reference may be hadto the following description taken inconn'ection with the accompanying drawingTin whichigure 1 is aperspective view of one type of apparatus embodying my invention; Fig. 2illustrates by means of curves some of the electrical characteristics ofthe device; Figs. 9 trating how the new device may be used in radiotelegraphic receiving systems.

As shown in Fig. 1 the discharge device comprises an inclosing envelop1, which may be of glass, inwhich are mounted, an electron-emittingcathode 2 and an anode 3. In the device illustrated both the cathode andanode consist of wire preferably of tungs'ten, tantalum, or other highlyrefractory metal which can be readily freed from ionizable gas. Theanode need not be a Wire but may be a plate properly freed from gas andit has been thus diagrammatically indicated in Fig. 3. The cathode 2 isa short V-shaped tungsten filament connected to terminal conductors 4, 5and supported at its bight by a hook 6, both the supply conductors andthe hooks 6 being mounted on a frame 7 so that the filament is locatedin a plane passing through the side arms of the frame.

The cathode supports 4., 5 and 6 are provided with small glass disks 8which reduce the tendency of a short circuit between the cathode and thegrid by vaporized metal deposited on the frame 7. Aroundthe outside ofthe frame is wound a wire 9 with closely spaced turns. This conductor 9commonly called the grid, serves'the purpose of varying the electricfield near the cathode and thereby varying the electron current betweencathode and the anode. The anode wire is conveniently supported by hooks10 located upon a forked glass support 11. The frame 7 and the support11 are mounted upon a glass stem 12 sealed into one end of the envelop:Leading-in conductors 13, 13 which supply heating current to the cathodeand the conductors 14, 14' which are connected to the terminals of theanode are sealed into the steml). in the usual manner. The anode isprovided with current connections at each terminal so as to enable it tobeheated duringthe evacuation of the de- 4t and 5 arediagrams ofconnections illusciently freed from gas without heating it by passage ofcurrent.

Before the envelop is sealed ofl' there is placed in it (in a mannerhereinafter de-' 'scrlbed) a small amount of vaporlzable material 17,forexample, an amalgam, sulfur, phosphorus pentoxid, tungstenhexachlorid, and in general substances having a, suitable vapor pressureat .the operating temperature of the device, Substances having too higha vapor pressure, for example, mercury, may be used if maintained duringoperation at a suitable low temperature, as in a side chamber. Gases atproper pressure will give the desired effect but the effective pressure,and possibly also the character of the gas arechanged by some chemicalor electrochemical action in the tube sothat gases act only temporarily.The material 17 is either loosely placed in the main envelop asindicated, or placed in a side chamber. The

character of this material, depends upon the temperature and voltagesatwhich the device is operated, as will be hereinafter explained, itspurpose being to maintain 1n the space, vapor at a. definite lowpressure.

For the evacuation ofthe device the glass walls of the tube are heatedso as tofree them from moisture and both the anode and the cathode areheated by passage of current so as to drive out the gases. When anamalgam is to be used as the source of vapor, the metal to beamalgamated, for,

example, silver, preferably is placed in the envelop before evacuation.The mercury is preferably placed in a side chamber which is kept coolduring the preliminary bakeout. The evacuation of the tube is carriedout by the'most approved methods of incandescent lamp exhaust, and thelast traces of gas are removed by either a Gaede molecular pump or bysome chemical evacuating means, such as the use of vaporized calcium ormagnesium. The last traces of ionizable gases are removed from theelectrodes by heating them to incandescence and preferably at the sametime operating the grid as the anode for an electron discharge, theimpressed voltage being. in-:

creased step by step as the gas is removed. After the parts of thedevice and the silver,

or other metal to be amalgamated has been freed from gas, mercuryvaporis permitted to diffuse into the envelop. For example, cleanmercury may be kept at a relatively low temperature in a side chamberduring the exhaust. When the exhaust is completed the mercury may bepermitted to reach room temperature or even a higher temperature, thusdifl'using into the main envelop to form silver amalgam. At roomtemperature one or two days are required for the amalgamation. Allexcess unalloyed A device thus prepared will operate at ordinary roomtemperatures with a substantially pure electron discharge l'ietweenanodeand cathode \vithoutpositive ionization, even when the impressedvoltage is as high as 300 to 4:00 volts, or even higher. However, whenthe voltage between anode and cathode is within a certain range anirregularity is observed in the electron discharge current, as alreadydescribed. This'voltage range is illustrated by curve 18 in Fig. 2,Which will be more fully understood by first considering the connectionsshown in Fig. 3. In this figure a-device 19 constructed as abovedescribed is connected in a secondary circuit of a transformer 20, theprimary of which is included in series with a condenser 21 ina groundedantenna circuit 22. -The grid 9 is connected by a conductor 23 to oneterminal of the transformer and the negative terminal of the cathode 2is connected through a potentiometer 24 and a conductor 25 to the otherterminal of the transformer secondary: Connected in shunt to thesecondary of the transformer is a variable condenser 26 so that byvarying either the capacity or inductance of the circuit it may be tunedto resonance with the incoming oscillations to be detected. The battery27 serves toheat the cathode to incandescence l current will flow intheplate circuit which will not affect the telephone receiver. Whenoscillations are received by the antenna and superimposed upon thepotential of the grid the electric fieldabout the cathode is changedcorrespondingly and a decrease of current is noted with each oscillationor series of oscillations, thereby producing sounds in the receiver.With a given electron detector it arkedly'fwith the grid potential,there "being a certain point at which the signals maybe most stronglyheard and a variation of grid potential above or below this valueproduces a decrease of audibility of the signals.-

In-Fig. 2 there are shown for the purpose of illustrationcurves of thecharacteristics of one particulardetector made in accordance with myinvention. For the curve 18 the ordinates represent-grid potentials withrespect to negative end of filament and the abscissze. the relayedcurrent in micro-amperes. The curve inldicates the current valuesobtained with a given terminal voltage between the cathode and the anodefor the indicated range of rid voltages with respectto the cathode. Thiscurrent is com monly known asthe plate-current. The sensitiveness of thedevice is indicated by curve 31 which is plotted with the ordinates ingrid potential and the abscissa in percentages of maximum sensitiveness.In other-words thiscurve indicates the degree of change in plate currentproduced by'impressed oscillations at difi'erent' grid potentie-1s.- Itwill be observed at 1.2 volts the curve-.cf sensitivenessreaches amaximum.

'It'avill also be observed that for a certain range of grid voltage oneach side of'this critical value, the plate currentexhibits anirregularity and then at higher gridvolt ages again increases at therate it had increased before the period of irregularity or off-set inthe curve.

' In the device here 1llustratedv a sudden change of grid potentialas-produced by impressed oscillations produces a' marked decrease ofcurrent in the plate circuit 28 providing the grid potential is not farfrom 1.2 volts positive. lVitha pure electron discharge devide such' asdescribed in Langmuir applicatiom'Serial No. ?95,610 an increase ofpositive grid potential-willproduce an increase of plate current. In theLangmuir device; a positive-impulse or charge on the grid produces acorresponding increase in the proportion of electron current taken bythe grid itself.

a On either side of the region of greatest sensitiveness indicated bythe. oil-set of the curve 18 of grid potential the characteristic "of mydevice is substantially that-ofa pure electron discharge. The vaporpressure necessary to produce the peculiar effect varies with thecharacter of the material used.

. For mercury vapor in the type. ofapparatus be obtained with theconnections illustrated by Fig. 3, my new detecting device may be usedin cascade with the pure electron discharge apparatus or relaydescribedin the Langmuir application above referred to.

Electrical connections suitable 'for thispurpose are shown in Figs. 4and 5.

In Fig. 4 the electron relay 32 has its grid'circuit'included in alocaltuned circuit 33, the various parts ofwliich correspond to thosedescribed in connection with Fig. .3. It need only be noted that thepotential of the grid is determined by a battery 34. The plate circuit35 contains a generator 36 or other suitable source of direct current ofdesired voltage; The variable plate current is impressed upon theprimary of an air core transformer 37, the secondary of which isconnected to the grid circuit 38 of a detector 39 made in accordancewith my invention The incon'ling'oscillations are magnified by the relay32 which produces in its plate circuit an amplified current similar incharacter to its received oscillations which is .then transformed anddetected as already described in connection with Fig. 3. In some casesthe relay 32 and my novel detector 39 may be to advantage coupledthrough a resistance 40 instead of a transformer, as shown in Fig. 5.

In the operation of my novel detector it is not necessary that thesource of current in the electrode circuit should be of invariablevoltage. An ordinary generator even though its voltage varies slightlydue to commutation. and soforth, may be used as indicated in Fig. 3.When using an audion a current source with a steady voltage is necessaryas an ordinary generator will cause noises in the telephone. The deviceis also less affected by static, or atmospheric disturbance's thandevices depending on gaseous ionization. It can be operated under themost sensitive conditions without the danger of'static causing thedischarge to burst into blue glow.

The high apparent resistance of the device renders changes ofresistances in the external circuit of little effect. For example, twoor three telephone receivers or more may beused in series in thereceiver circuit Without any noticeable change in the loudness orclearness of the signals.

' What I claim as new and desire to secure by Letters Patent of theUnited States, is

1. An'electrical discharge device comprising a gas-tight envelop and anelectronemitting cathode and an anode, the space withinsaid envelopbeing evacuated to such degree that current conduction can take placefrom cathode to anode bymeans of cathode while carrying currentindependently of gas conduction.

2. A device for detecting high frequency oscillations comprising acathode adaptedto be heated, an anode, a grid located near said cathode,an inclosing envelop, and means for maintaining within said envelop gasat a substantially constant pressure at which the device possesses aregion of maximum sensiti'veness to oscillations impressed on said gridwhen said grid is at a critical potential with respect to the cathode,the gas pressure being so low that a discharge between cathode and anodeis substantially independent of positive ionization at grid chargesmaterially more positive than said critical potcntial.

3. A detector for high frequency signals comprising a highly evacuatedenvelop, a

cathode adapted to be heated to incandescence, an anode, adischarge-controlling conductor, and means for maintaining insaidenvelop gas of such character and pressure that there is a decreaseconductivity for variations ofpotentials of the discharge controllingconductor from a critical potential, the electrodes of said device beingfreed from gas so completely and the gas pressure therein being so lowthat the electrical characteristics at current values both lower andhigher than the critical region substantially follow the law of pureelectron conduction.

4. An electrical discharge device comprising an envelop, anelectron-emitting cathode, an anode, a discharge-controlling conductorlocated near said cathode, said device being deprived of gas to suchdegree as to be capable of operation with a substantially pure electrondischarge at several hundred volts and a vaporizable substance in saidenvelop.

5. A device for detecting high frequency oscillations comprising anenvelop, a cathode adapted to be heated to incandescence, an anode,means for varying the electrical field of mercury and silver in saidenvelop.

6. An electrical discharge device compris ing an envelop, anelectron-emitting cathode,

an anode, the interior of said envelop being deprlved of gas to such lowpressure that positive ionization is substantially absent when normallyoperating and a substance in said envelop exposed to the evacuated spacehaving a vapor pressure of about six to forty hundred-thousandths of amillimeter of mercury.

7. An electrical discharge device'comprising an envelop, anelectron-emitting cathode, an anode, the interior of said tube beingdeprived of gas to such low pressure that positive ionization issubstantially absent at impressed terminal potentials of several hundredvolts, and an amalgam in said envelop exposed to the evacuated space,said amalgam having a vapor pressure at ordinary temperatures of about.00006 to .0004 millimete'rsof mercury.

8. The method which consists in produc- "ing an electron discharge in aspace evacuated to such degree that positive ionization of gas presentin said space is absent, supplying to said space gas at a constantpressure too low to cause appreciable ionization but high enough tocause a sudden decrease of electron current when the electrical fieldnear the cathode is increased or decreased by high frequency waves.

In witness whereof, I have hereunto set my hand this 19th day of March,1914.

WILLIAM 0. WHITE

